Boil the water with the sugar so that the sugar dissolves. Add citric acid. Place the first 12 stalks of peppermint in the hot mixture until they turn brown - this is done pretty quickly. Then take it out.
After cooling, insert the next 12 stalks and let them steep overnight. Replace with 12 fresh stems the next day.
In the evening, remove the stems and place the lavender inflorescences in for about 4 hours. Take out and fill the syrup in bottles.